The invention relates to a device for cleaning a cylinder of a machine for processing printing material, having a cleaning cloth pressable onto the cylinder for forming a contact zone, and a first monitoring zone disposed downstream of the contact zone, in a travel direction of the printing material. The first monitoring zone is monitorable with regard to a faulty position of the cleaning cloth.
In particular, the machine for processing printing material is a rotary offset printing machine, and the cylinder is a blanket cylinder of the rotary offset printing machine.
During the cleaning of such a blanket cylinder, the cleaning cloth may remain stuck to the circumferential surface of the blanket cylinder and, because of the rotation of the blanket cylinder, may be pulled in a direction towards a cylinder nip formed by the blanket cylinder together with a printing plate cylinder. For the case wherein the cleaning cloth is, in fact, pulled into the cylinder nip, more or less critical complications have to be expected. Consequently, precautions should be taken for ensuring at least that the cleaning cloth is not pulled too deeply into the printing press and that the section of the cleaning cloth pulled into the cylinder nip is only a relatively short section, respectively.
The published European Application EP 0 291 745 B1, corresponding to U.S. Pat. No. 4,867,064, describes a device corresponding to the general type described at the introduction hereto, wherein the precautions required for protecting against the accident described hereinabove are taken. The device is equipped with a multifunctional element which, on the one hand, serves as a cutting blade for cutting up the cleaning cloth and, on the other hand, as a monitoring element for sensorially monitoring the monitoring zone lying between the contact zone and the cylinder nip. When such an accident occurs, the cleaning cloth is cut up by the multifunctional element and, thereby, the length of the section pulled into the cylinder nip is limited. In addition, the multifunctional element actuates an emergency stop switch which serves as a sensor and which prevents the section cut from the cleaning cloth from being pulled too deeply into the printing press, and by which assurance is provided that the section can be removed from the printing press again without very great effort.
The device operates reliably, however, only if the direction of rotation of the blanket cylinder, which is represented by an arrow A in FIG. 4a of the cited patent is maintained. If rotation should take place in the opposite direction of rotation, this would certainly rule out any possibility that the cleaning cloth adhering to the blanket cylinder would be pulled into the cylinder nip formed between the blanket cylinder and the printing plate cylinder, but instead, the danger would arise that the cleaning cloth might be pulled into another cylinder nip, specifically into the nip which is formed between the blanket cylinder and an impression cylinder. Changing the direction of rotation of the blanket cylinder during the progress of a cleaning program is therefore not possible for safety reasons. The precautions against the accident, which are associated with the device, are inadequate and permit only the rotation of the blanket cylinder to be performed in the rotational direction represented by the arrow A during the cleaning of the blanket cylinder.
It is accordingly an object of the invention to provide a cleaning device for a cylinder of a printing-material processing machine, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which has improved precautions against accidents.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for cleaning a cylinder of a machine for processing printing material, comprising a cleaning cloth pressable onto the cylinder for forming a contact zone. A first monitoring zone is monitorable with regard to a faulty position of the cleaning cloth. The first monitoring zone is disposed downstream of the contact zone in a travel direction of the printing material. A second monitoring zone is disposed upstream of the contact zone in the travel direction of the printing material. The second monitoring zone is monitorable with regard to another faulty position of the cleaning cloth.
In accordance with another feature of the invention, the cleaning device further comprises at least one monitoring element which, with a sensor coupled therewith, is assigned to the monitoring zones.
In accordance with a further feature of the invention, the sensor is assigned both to the first monitoring zone for registering the first-mentioned faulty position, and to the second monitoring zone for registering the other faulty position.
In accordance with an added feature of the invention, the monitoring element is a tensioning element.
In accordance with a concomitant feature of the invention, the tensioning element is formed with a deflection therein.
The object of the invention is thus attained by providing a device for cleaning a cylinder of a printed material processing machine having a contact zone. A first monitoring zone is disposed downstream from the contact zone in a travel direction of the printed material. The first monitoring zone is controlled or monitored by a sensor with regard to a first faulty position of the cleaning cloth. A second monitoring zone is disposed upstream from the contact zone in the travel direction of the printed material. The second monitoring zone is controlled or monitored by a sensor with regard to another faulty position of the cleaning cloth.
In the device according to the invention, the monitoring zones located on both sides of the contact zone are monitored by a sensor with respect to the faulty positions, for example loop formations, of the cleaning cloth which are typical of such faulty position accidents.
Thus, a change in the direction of rotation of the cylinder performed during the cleaning process is advantageously possible without risk. The change in the direction of rotation can be provided, for example, within the context of performing a washing process already described in the German Published Non-prosecuted Patent Application DE 195 08 569 A1, corresponding to the British Patent 2 289 438 assigned to the same corporate assignee as that of the instant application, the washing process being particularly thorough.
Various developments of the cleaning device according to the invention are possible:
For example, the first monitoring zone may have a first monitoring element assigned thereto, and the second monitoring zone may have a second monitoring element assigned thereto.
The first monitoring element can be coupled to a first sensor, and the second monitoring element can be coupled to a second sensor.
If contactless registration of the faulty positions is provided, the first monitoring zone can be monitored by a first light barrier and the second monitoring zone by a second light barrier. In this case, transmitters (radiation sources) of the light barriers function as the monitoring elements, and photoelectric receivers as the sensors. The transmitters and receivers, respectively, are coupled with one another by radiation and optically, respectively.
However, tactile registration or determination of the faulty positions can also be provided, by constructing the monitoring elements as contact elements. Contacts with the contact elements by the cleaning cloth effects a registration or determination of the faulty positions.
If the first monitoring zone has the first contact element and the first sensor assigned thereto, and the second monitoring zone has the second contact element and the second sensor assigned thereto, then the first contact element can be mechanically coupled with the first sensor, and the second contact element can be mechanically coupled with the second sensor.
Instead of the first sensor and the second sensor, however, only a single sensor assigned jointly to the contact elements can also be provided, with which each of the two contact elements is mechanically coupled.
Each of the two sensors and also the common sensor may be a displacement transducer or a force transducer or an electric switch.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for cleaning a cylinder of a machine for processing printing material, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.